Solvent dewaxing and extracting of petroleum oils



Patented Mar. 8, 1938 UNITED STATES PATENT OFFICE SOLVENT DEWAXING AND EXTRACTING F -'PETROLEUM OILS No Drawing. Application November 2, 1934, Serial No. I751,257

2 Claims.

This invention relates to solvent dewaxing and extracting of petroleum oils; and it comprises methods of dewaxing and extracting such oils with solvents wherein the oil is mixed, at ordinary 5 temperatures, with a solvent of low viscosity, miscible with the oil at dewaxing temperatures, the mixture is cooled to dewaxing temperatures, the precipitated wax is removed from the oil, the oil diluted with said solvent so obtained is then mixed with an additional solvent miscible with the first solvent and capable of forming a mixed solvent therewith which behaves as a differential solvent having a miscibility temperature sufficiently low to cause separation of an oil layer at about dewaxing temperatures, and finally separating the oil layer and solvent layer so formed, the oil layer being freed of residual solvents to recover an improved'dewaxed refined oil; all as more fully hereinafter set forth and as claimed.

Petroleum oils primarily are composed of parafiinic oils, naphthenic and polynaphthenic oils and petrolatum which is a mixture of high and low melting waxes with resins; It is known that by dewaxing the oil and removing the 5 naphthenic oils, improved oils can be obtained.

Petroleum oil being more or less a heterogeneous mixture, its behavior when treated with solvents varies with the particular solvent. Some solvents such as benzol and naphtha are completely miscible with the oil but when the solution is cooled the waxes or petrolatum become insoluble at certain temperatures and may be separated from the oil diluted with the solvent. Such solvents are known in the art as good solvents because they hold the oil in solution even at low temperature.

On the'other hand there is another class of solvents which are not completely miscible with the oil. Such solvents when admixed With the oil at elevated temperatures do form homogeneous miscible mixtures. But when the mixture is cooled, it stratifies into anoil layer and a solvent layer. The naphthenic portion of the oil, is soluble in'these solvents'and appears in the solvent layer. The parafiinic oils are insoluble and constitute most of the oil layer when it is formed. Such solvents are known as differential solvents. It has been proposed to dewax petroleum oils by mixing the oil with good solvents and cooling the mixture to precipitate the wax. The wax is separated from the oil diluted with solvent either by filter pressing or centrifuging.

Likewise, it has been proposed to refine oils by" solvent extraction using the other type of solvents which function as differential solvents. In these solvent extraction processes the oil and the solvent are mixed and then the mixture brought to temperatures at which the oil layer and the solvent layer are not miscible. The oil layer is separated from the solvent layer containing extracted naphthenic oil and the oil layer freed of residual solvents.

Although it is necessary to both remove the Wax and the naphthenic bodies to obtain -a completely refined oil, heretofore no single process was available by which both of these refinements could be obtained in a simple unitary manner. Of course, the oil could be first dewaxed and then refined or vice versa, but each of the procedures is entirely independent of the other and constitutes a separate process. Further, the prior dewaxing and solvent extraction processes in commercial practice are subject to one or more disadvantages or difiiculties. In any event, in prior practice, it was necessary to completely remove the dewaxing solvent before proceeding with the solvent extraction or vice versa to avoid com; plications.

By the present invention we obtain a substantially complete refining of the oil in an improved manner which is free of the disadvantages and difiiculties of the prior methods. In the present process the dewaxing and the solvent extraction are effectively correlated in a unitary simple process having many advantages.

In the present unitary complete processes, the oil is first dewaxed in the presence of certain solvents and then after the wax has been separated and without removing the dewaxlng solvent, the dewaxed oil is extracted by means of a mixed solvent. The mixed solvent is a composite mixture of dewaxing solvent with another solvent, the two solvents being so correlated that the mixture behaves as a differential solvent under conditionshere employed. By operating in this way as is hereinafter more fully described, the dewaxing and the solvent extraction become a unitary complete method instead of two separate and independent refining methods asheretofore employed in the art.

We have found that oils diluted with solvents may be satisfactorily dewaxed at temperatures from about '+10 F. to 40,F. in most .cases. In the present processes dewaxing can be advantageously effected at such temperatures. The dewaxing solvent which may be designated solvent A is one which has a low viscosity and is miscible with the oil at dewaxing temperatures. Solvent A may be any one of the solvents known Petroleum naphtha is a typical member of the class of good solvents for the oil and may be used as solvent A in the present processes. Ethylene dichloride is also useful as solvent A in these proceses. Solvent A is not necessarily limited to single solvents. Mixtures'of solvents behaving in the manner specified may be used. For instance,

mixtures comprising ethylene dichloride and benzol, ethylene dichloride and carbon tetrachloride, acetone and benzol, etc., may be used. Any solvent or mixture of solvents which will hold the oil in solution at dewaxing temperatures and dilute the oil to give a freely mobile liquid easily drained from the precipitated Waxes is useful.

As stated ante, the extraction solvent used in these processes is a composite solvent containing solvent A as one constituent thereof. The other constituent of the composite extraction solvent may be designated as solvent B. Various solvents may be used as solvent B provided they have certain characteristics. First solvent B must be miscible with solvent A at the temperatures here used. Solvent B must, when mixed with solvent A, form a composite solvent which behaves as a difierential solvent. The miscibility temperature of the composite solvent with respect to the oil should be such that stratification into an oil layer and a solvent layer is obtained at about dewaxing temperature. That is, the composite solvent used has a miscibility temperature equal to or higher than the temperatures employed for dewaxing. With such composite differential solvents the extraction of the oil may be effected without the necessity of further cooling the filtrate obtained from the dewaxing operation. This together with the fact that the dewaxing solvent does not have to be removed prior to solvent extraction makes the present processes particularly advantageous.

Advantageously, solvent B itself may be a differential solvent. For instance we may use ethyl or methyl ether of ethylene glycol (known to the trade as Cellosolve and Methyl Cellosolve, respectively) furfural and nitrobenzene as solvent B. Sulphur dioxid is particularly advantageous in these processes as solvent B.

In these processes, of course, the solvent B must be correlated with solvent A to give the desired results. By proper selection and correlation of solvents A and B, particularly advantageous embodiments of this broad invention may be obtained to meet unusual refining problems as well as improved standard refining practice.

Ethylene dichloride as solvent A and furfural as solvent B is an effective combination. Another satisfactory combination is ethylene dichloride as solvent A and nitro benzene as solvent B. Still another is ethylene dichloride as solvent A and methyl cellosolve as solvent B. The use of sulphur dioxid as solvent B is advantageous. It may be used in conjunction with ethylene dichloride, ethylene dichloride-benzol, ethylene dichloride-carbon tetrachloride or acetone-benzol, as solvent A to advantage.

In practicing the present invention a suitable amount of solvent A is mixed with the oil at ordinary temperatures and the mixture is cooled to temperatures suflicient to render the wax in-' -to give a fluid oil solution at the dewaxing temperatures; one which is sufficiently mobile to readily drain off from the wax. When a differential solvent is used as solvent A, it should not throw down any good oil at dewaxing temperatures for otherwise the precipitated wax will be contaminated with a little oil. This can be avoided if in selecting the differential solvent to be used as solvent A a solvent is chosen which has a miscibility temperature substantially below the dewaxing temperature to be employed. Also when differential solvents are desired as solvent A, the danger of leaving a small residue of oil with the wax can be avoided by adding an appropriate amount of good solvent for the oil to give a composite solvent for use as solvent A. For instance, ethylene dichloride can be admixed with minor amounts of benzol to give such a composite solvent A. Then the cooling can be as low as 20 F. without any separation of oil during the dewaxing.

Generally, 3 to 4 volumes of solvent A to one volume of oil is satisfactory. Of course the amount and kind of solvent selected for solvent A should be correlated with the solvent B which is to be used so that when the solvent B is added after the dewaxing step an appropriate amount of composite extraction solvent is formed, so as to obtain efiicient extraction of naphthenic bodies from the parafiinic oil. By proper correlation, the minimum amounts of solvent for each of the steps can be readily adjusted to avoid an excess in either of the steps.

After the wax has been precipitated and removed, the filtrate which comprises the oil diluted with solvent A is then ready for solvent extraction.

It is merely necessary to add the selected solvent B to the cold filtrate from the dewaxing operation. Then the mixture is permitted to stand at about the dewaxing temperature until clean stratification is obtained. Then the oil layer is separated from the solvent layer. The

oil layer is then distilled to remove the residual solvent. An improved dewaxed refined oil is obtained. The solvents so removed may be separately recoveredfor re-use in the process. Likewise the solvents are recovered from the solvent layer. As a by-product from the solvent layer there is obtained a useful naphthenic oil. A continuous countercurrent process may be used.

In operating in the manner described in a sense, solvent A dissolves all of the oil and the addition of solvent B precipitates the good oil from the mixed solution. By such a procedure effective contact of the differential solvent with the oil is obtained and a highly selective, substantially complete extraction is obtained in a simple manner. Practically all of the naphthenic bodies are quickly removed with a minimum loss of good oil. Of course, the amount of solvent B added will vary according to the conditions used in a particular embodiment. The amount added should be suflicient to cause a clean stratification giving a volume of composite differential solvent suificient to extract the naphthenic content of justed to the amount and type of solvent A present as Well as to the volume of oil being processed.

As stated, various embodiments of this invention may be used in practice. The following examples are advantageous embodiments typical and illustrative of the present invention:

Example 1 100 parts of unpressable wax distillate from Oklahoma crude is mixed with 300 parts of ethylene dichloride at about F. The mixture is cooled to 15 F. over a period of one hour. The cooled mixture is filter pressed at this temperature. The cold filtrate is mixed with 150 parts of furfural and permitted to stand until a clean stratification is obtained. During this standing the temperatureis kept constant at approximately 15 F.

The oil layer is separated from the solvent layer and then freed of residual solvents by distillation. The removed solvents are distilled in a column still to separately recover the solvents.

By the above method, 39.2 parts of an improved dewaxed refined oil are obtained. The improvement obtained by this procedure is shown by comparison of the following properties of the Wax distillate and the refined oil:

Refined Original Oil Specific gravity, 60 F 0.918 0.8959 Viscosity, Saybolt 210 F sec 73 73.5 Viscosity index 59 7'7 Viscosity-gravity constant 0.856 0.823 Carbon residue 1.35 0.3 Pour point, F 10 The solvents are likewise recovered from the solvent layer yielding 25.2 parts of useful naphthenic oil. The removed solvents were separately recovered for re-use in the process.

Example 2 .mixture is permitted to stand until clean stratification is obtained. The oil layer is separated from the solvent layer and freed of residual solvents by distillation; 55 parts of refined oil are obtained.

The improvement obtained by this method is shown by comparison of the following properties of the overhead cylinder stock and the refined oil:

Refined Original Oil Specific gravity, 60 F 0.927 0.8957 Viscosity, Saybolt 210 F sec 130 104 Viscosity index 70 89 Viscosity-gravity constant 0.853 0.815 Carbon residue 2.05 0.35 Pour point, F 110 10 The solvents are likewise recovered from the solvent layer yielding 20.5 parts of useful naphthenic oil. The removed solvents were separately recovered for re-use in the process.

Example 3 parts of overhead cylinder stock from 0klahoma crude is mixed with 300 parts of 70-30 ethylene dichloride-benzol mixture at 75 F. and the mixture is cooled to 0 F. over a period of one hour. The cooled mixture is filter pressed at this temperature.

The col-d filtrate so obtained is mixed with 300 parts of nitrobenzene and the mixture allowed to stand one half hour at 0 F. to permit clean stratification. The lower oil layer is then drawn off and the refined dewaxed oil recovered from the upper oil layer by distilling oif the solvent. 30.8 parts of refined oil are obtained.

The. improvement obtained by this method is shown by comparison of the following properties of the overhead cylinder stock and the refined oil:

Refined Original Oil Specific gravity, 60 F 0.927 0.8829 Viscosity, Saybolt, 210 F sec 130 94.5 Viscosity index 70 97 Viscosity-gravity constant 0.853 0.800 Carbon residue 2.05 0.15 Pour point, F 10 The solvents are likewise recovered from the solvent layer yielding 42.8 parts of useful naphthenic oil. The removed solvents were separately recovered for re-use in the process.

What we claim is:

1. As an improved, unitary process for dewaxing and solvent extracting petroleum oils, the steps which comprise first dewaxing the oil by admixing the oil with acetone and benzol, cooling the mixture to precipitate the Wax and separating the wax from the cold oil diluted with the solvent mixture and then solvent extracting the naphthenic bodies from the dewaxed oil by adding sulfur dioxide to the cold solution from the dewaxing operation in suificient amount to effect a stratification of the mixture into an oil layer and a solvent layer at approximately the dewaxing temperature and separating the oil layer from the solvent layer thus formed.

2. The improved process of refining oils which comprises admixing the oil with a 65:35 mixture of benzol and acetone at about 75 F., cooling the mixture to approximately 4 F. to precipitate the wax contained in the oil, separating the wax from the oil diluted with said composite dewaxing solvent at said temperature, adding to the cold filtrate so obtained sufiicient sulphur dioxid to effect stratification into an oil layer and a solvent layer, separating the oil and solvent layers so obtained and removing residual solvent from the oil layer to obtain an improved dewaxed refined oil.

ERIC B. HJERPE. WILLIAM A. GRUSE. 

